Effects of sustained axial load and cooling phase on post-fire behaviour of reinforced concrete stub columns

• The sustained preload led to significant residual deformations of RC stub columns.
• The preload and cooling phase have significant effects on mechanical behaviour of fire-damaged RC columns.
• The effects on residual axial stiffness and ductility are more remarkable than that on residual strength.
• The preload effect should not be ignored while assessing the behaviours of fire-damaged concrete structures.

In this paper is presented an experimental investigation of the effects of preload and cooling phase on the residual strength, stiffness and ductility of reinforced concrete stub columns which were heated and cooled down to room temperature under sustained axial load. Reinforced concrete stub columns were axially loaded and heated to designed temperatures in a specially built electrical furnace. After the specimens cooled down to ambient temperature with the axial loads kept constant, the stub columns were loaded to failure. The sustained preload led to significant residual deformations of reinforced concrete stub columns during the cooling phase. The test results showed that the mechanical behaviour of the fire-damaged reinforced concrete stub columns with preload was remarkably different from those without preload. The sustained axial loads resulted in obviously increased strength and stiffness during the loading phase, but reduced stiffness and deteriorated ductility in the unloading phase. Based on the test results, it is recommended that the effects of sustained axial loads during the fire and cooling phase should be taken into consideration in assessing the fire-damaged reinforced concrete columns.